1. Field of the Invention
In incineration systems for the incineration of refuse, it is generally desirable that both the exhaust gases and also the particulates, that is flue dust and ashes, are burned as completely as possible. The energy generated during such an incineration process can often be utilized for additional functions, such as generating steam for operating a turbine, etc. In order to insure that the incineration process is efficient, it can be desirable to regulate the quantity of refuse or the depth of the refuse layer on the grates within a refuse incinerator system.
2. Background Information
The grate disclosed in German Patent No. DE 24 46 724 C 3 can be considered an example of one type of incinerator grate which can be used for the incineration of refuse. The grate described therein consists of several grate zones, which comprise both stationary and movable grate bars which overlap one another like roof tiles. The movable grate bars of one zone are simultaneously hydraulically retracted and advanced, to move the charge through the furnace and also to rearrange the charge. To achieve a uniform transport of the charge, all the grate bars are moved at essentially the same speed. The present invention is, however, not restricted to only the combustion grates as disclosed by DE 24 46 724 C 3.
The operation of a refuse incinerator is particularly difficult, in comparison to the operation of coal-fired, oil-fired or gas-fired systems, because the fuel, i.e. the refuse, varies in terms of its composition and combustion properties. The operation of a refuse incinerator can therefore be subject to constant and sometimes extreme fluctuations.
In order to provide approximately constant incineration conditions and safe and reliable operation, essentially constant adjustments of the firing as a function of the fuel which is introduced need to be made. Some of the considerations which can affect the firing conditions include differences in piece size, density, moisture content, net calorific value and flammability of the refuse being burned.
Now and in the future, the principal objective of refuse incineration is the disposal of refuse and the processing of recyclable materials. Therefore, the primary emphasis should essentially be placed on the reduction and elimination of harmful or toxic substances. The energy generated is no longer an urgent necessity, but remains a desirable byproduct.
The most important objective of the incineration should therefore be considered to be the burning of both the exhaust gases and also the particulates, that is, flue dust and ashes, as completely as possible.
These requirements can ultimately only be met by maintaining approximately constant operating, or combustion conditions during the incineration process. Compliance with new legal requirements makes the maintenance of constant combustion conditions increasingly important.
It is known that the incineration of refuse which entails severe fluctuations in calorific value tends to overload or underload the grates. For example, if the calorific value of the refuse decreases on account of an increased proportion of wet or inert material, the heat released and the quantity of steam generated are typically also reduced. Therefore, in order to compensate, additional refuse is typically added to the combustion chamber, whereby the grates can become overloaded.
An incineration regulation system which aims at constant steam production will therefore typically increase the amount of refuse charged into the incinerator when there is a decrease in the calorific value of the refuse. But, as mentioned above, this hcan often lead to an overloading of the grate, and instead of the desired increase in temperature, there can instead be a further reduction of the combustion chamber temperatures, as insufficient burning may result. Moreover, such an overloading can tend to lead to a "trash heap" on the grate, which trash heap can be transported through the incinerator and can ultimately results in ashes which are incompletely burned.
On the other hand, when the refuse has a high net calorific value, the typical response is to decrease the amount of refuse being fed onto the grates, to attempt to bring about a reduction in the heat being generated. However, when the refuse feed is decreased, there can be a danger that if the amount of refuse charged into the incinerator is excessively reduced, there will be "holes" in the layer of refuse on the grate. Such "holes" can results in the escape of cold combustion air, along with plumes of CO, through the layer and up the exhaust stacks.